1. Field of the Invention
The present invention relates to the manufacture of plastic bags or packages having at least two plies of thermoplastic sheeting, both plies having closure strips formed or included on their facing inner edges so as to form a snap fastener-like closure for the openings of the bags or packages made therefrom.
2. Description of the Prior Art
The present invention relates to improvements in the package-making art and may be practiced, without limitation, in the manufacture of thermoformed bags and thermoformed trays of the kind that may be used for various consumer products, but which are particularly useful for food products which should be kept in substantially air-tight packages, free from leakage until opened for access to the product contents, which packages are desirably reclosable by zipper means to protect any remainder of the product therein.
The indicated art is fairly well developed, but nevertheless is still susceptible of improvements contributing to increased efficiency and cost effectiveness.
One problem that still exists in the production of packages from continuous zipper-equipped sheet material, such as film, especially where the film and zipper are separately formed and then joined, resides in the difficulty in dividing the zippered film into package-oriented sections, because the zipper is of greater mass than the film.
Another problem is represented by the difficulty in attaining a satisfactory sealing of the zipper against leakage, where the zipper and the area of film engaged by the zipper extends through the side seal areas separating one bag or package from the next.